In gas turbine engines the tailcone and exhaust guide vanes become hot as a result of the turbine exhaust gases passing thereover. As a source of infra-red radiation these provide a target source for heat-seeking missiles. A reduction of the temperature when in the non-augmented mode is therefore desirable.
In an augmented turbofan engine it is usual to supply fan air to the augmentor. This fan air continues whether or not the augmentor is in operation since it mixes with the core flow gases and aids in engine thrust.